A pressure-sensitive adhesive label constructions comprises a laminate of a facestock or backing, a layer of a pressure-sensitive adhesive and a release liner providing a release surface for the pressure-sensitive adhesive.
In tape constructions, a release is applied to the side of the facestock or backing opposed to the side in contact with the pressure-sensitive adhesive to provide the release surface which enables the facestock and pressure-sensitive adhesive to be peeled away from a contiguous layer of facestock and adhesive.
Pressure-sensitive adhesives (PSA) normally fall into one of two categories, permanent and removable.
Permanent pressure-sensitive adhesives are adhesives which have a level of adhesion which does not allow the removal of the label from the substrate to which it has been applied without considerable damage to a paper facestock such as tearing or for stronger facestocks such as polyester, suffering failure at the facestock, cohesive failure in the body of the adhesive or leave a significant amount of adhesive on the substrate.
The adhesion of removable pressure-sensitive adhesives is considerably lower, allowing removal of the facestock or label with adhesive from the substrate even after a protracted period of contact. Removal is without significant damage to the facestock or substrate. Typically, a removable pressure-sensitive adhesive will have a bond of about 50 to about 300 N/m to stainless steel.
The limitation on the use of removable pressure-sensitive adhesives for the tape and label constructions is that a primer is needed to enable adequate anchorage to the facestock and, for some removable pressure-sensitive adhesives, to prevent staining of paper facestocks.
Traditionally the primer has been deposited as a barrier coat from a solution of a polymer in an organic solvent such as toluene. Ethylene-vinyl acetate and styrenic polymers both filled and unfilled have been employed.
Environmental considerations, however, have mandated a reduction in the amount of solvent employed in industry.
Aqueous, emulsion-based primers for facestocks have been tried as replacements, but impart curl to a paper facestock. Curl can be removed by remoisturizing the paper but at an additional cost. Many papers, moreover, have a glossy surface and remoisturization reduces gloss and the quality of the product is adversely affected. This is not acceptable in industry.
In addition, many coaters do not have a primer-coating station or an oven to dry the primer coat. It would be desirable, therefore, to provide an alternate route to providing removable pressure-sensitive adhesive constructions which would not involve the use of solvent-based primer systems.
Dual and multiple die coatings on substrates are well known in the art and described for instance in U.S. Pat. No. 3,573,965 incorporated herein by reference.
U.S. Pat. No. 4,260,659 to Gobran, incorporated herein by reference, describes a multilayer pressure-sensitive adhesive tape formed of a plurality of superimposed pressure-sensitive adhesive strata the outer strata of which being significantly softer than the strata immediately underlying it.
U.S. Pat. 4,854,259 to Kuller, incorporated herein by reference, describes a process for producing a pressure-sensitive adhesive tape comprising a plurality of concurrently coated superimposed layers, at least one outer layer of which being a pressure-sensitive adhesive layer, with contiguous layers defining an inner phase therebetween each layer comprising a photo polymerized matrix of polymer chains extending from matrix of one layer through the interface to the matrix of a contiguous layer. As consequence thereof, the layers cannot be delaminated.
The current method of manufacture of a removable pressure-sensitive adhesive label stock is depicted in FIG. 1. With reference thereto a facestock or backing web is coated with a primer from a solvent and oven dried to form a web of primed backing. Contemporaneously, a web of release liner is coated with a removable pressure-sensitive adhesive, which is oven dried. The laminate of removable pressure-sensitive adhesive and the release liner is combined with the formed primed facestock to form a final laminate of facestock, primer, removable pressure-sensitive adhesive and release liner. It is also feasible to apply the removable PSA directly to the primer and laminate that subassembly to the release liner. For tape constructions the release liner is eliminated and a release agent is applied to the surface of the backing opposed to the surface in contact with the removable pressure-sensitive adhesive.
This is a multi-step and costly process and it would be desirable to make the construction of removable pressure-sensitive adhesive product less costly without jeopardizing the performance of the removable pressure-sensitive adhesive. This is the subject of the instant invention.